No, I'm not an inmate.

I want to dig a tunnel for some 3" PVC, roughly 5' below grade (12' long). I
don't relish lifting the paving stones (again) or digging a trench 5' deep.
So I'm wondering how successful the water drills really are? I've read good
things, but it seems too good to be true. There's also a chance that the
area contains fill with the odd piece of concrete/brick. If I use a 3/4"
pipe with couplings I don't imagine I can hope for more than an 1.5" hole?

There's also these bad boys:

http://www.customaugers.com/alpha.html

But one long enough to do the job would break the budget. I've checked the
rental (Toronto) places online, but I haven't seen any yet.

Any words of wisdom on the water drills or better ideas?